1. Field of the Invention
The present invention is directed to a liftgate apparatus.
2. Description of the Related Art
Liftgates may be attached to vehicle trailers or other forms of vehicle cargo holds to assist with loading and unloading. In general, liftgate apparatuses include a platform or deck and a motorized system that is used to move the platform. There are several types of liftgate apparatuses, including a rotating platform apparatus and column type lift apparatuses which include rod screw type lift apparatuses and sliding bar column lift apparatuses.
The rotating platform apparatus may include a relatively small platform which, in the stored position, may serve as the rear enclosure for the vehicle, may fold up behind the rear enclosure, or may fold up underneath the back of the vehicle. Its vertical height limitation is usually the height of the bed of the trailer and is approximately four feet above ground level. Typically, this type of liftgate apparatus may include hydraulic cylinders hooked to control arms or levers. Thus, this type of liftgate apparatus is very limited in its vertical capabilities. Furthermore, the relatively small “footprint” or size of the platform means that large items, for example, automobiles, cannot be placed on the platform to be raised.
Column type liftgate apparatuses typically use hollow columns, placed vertically, one on each side of the back of the vehicle. Unlike the rotating platform apparatus, the column type liftgate apparatuses may be raised to as much as ten feet above ground level. The rod screw type liftgate apparatuses may include a machined rod screw placed vertically inside the column and which can be turned clockwise or counterclockwise. Grooves may be machined in the rod screw along its length, giving it the appearance of a barber pole. Ball joints with similar grooves may be fitted inside the rod screw grooves so that as the rod turns clockwise or counter-clockwise, the ball joints may move up and down. The platform may be attached to this ball joint and thus moves vertically as the ball joint moves up and down. A major drawback of this type of liftgate apparatus is price. This type of liftgate apparatus also requires skilled personnel for operation.
Sliding bar column liftgate apparatuses replace the rod screw with a sliding bar approximately five feet long in each column. These sliding bars may move vertically inside the hollow column by means of friction slides or rollers. They are typically attached to hydraulic cylinders one of each side, mounted vertically inside the columns. As the hydraulic cylinders extend, because they are attached to the sliding bars, they raise or lower the sliding bars which are also attached via a hinge to the liftgate. With telescoping cylinders, this type of liftgate can reach heights of approximately eight feet above ground level. Two or more people are typically required to open and close this device. Because the slide bars of this type of liftgate extend beyond the roof of the attached vehicle, one side tends to get ahead of the other causing jamming. Furthermore, with the cylinders in the rear, this type of liftgate can add 12 inches or more to the length of the attached vehicle. There are also problems typically associated with maintenance and access of these types of apparatuses.
With traditional liftgates of both screw and slide bar types, the liftgate must be rotated into position underneath an overhanging roof, then raised vertically against a rubber or similar type seal so that the roof and seal can prevent air or rain leakage to the inside of the vehicle. Because some of these prior art devices utilize friction guides beside the slide bars, friction is created by these guides or spacers. As a result, in these prior art devices the liftgate may stop moving just before it is fully closed and the liftgate cannot be opened or closed without application of physical force. Therefore, when being closed, these prior art devices require physical force by one or more men to push the gate closed as another individual works the hydraulic controls to raise the gate under the overhanging roof. To open the gate, men must go inside the truck/trailer and push the gate outward from the inside after it is lowered out from under the overhanging roof. Thus, in these prior art devices a single individual cannot operate these liftgates.